1. Field of the Invention
This invention relates to methods for producing patterned films of metal-containing materials on a substrate. More particularly, the methods of the present invention relate to a positive metal organic deposition process for producing patterned films of metal-containing compounds on a substrate through photochemical reactions, photothermal reactions or a combination thereof.
2. Description of the Related Art
The semiconductor and packaging industries, among others, utilize thin metal and metal-oxide films in their products. Examples of conventional processes used to form such thin metal and metal-oxide films include evaporation, sputter deposition or sputtering, chemical vapor deposition (“CVD”) and thermal oxidation.
Evaporation is a process whereby a material to be deposited is heated near a substrate on which deposition is desired. The process is normally conducted under vacuum conditions and comprises vaporizing the material to be deposited and condensing that material on the substrate. A screen or shadow can be used to pattern a film of the desired material on the substrate. Unfortunately, evaporation has several disadvantages such as the need for high temperatures and high vacuum conditions.
Sputtering is a process similar to evaporation and comprises vaporizing a material to be deposited on a substrate by bombarding the material with incident atoms of sufficient kinetic energy such that particles of the material are dislodged into the vapor phase and condensing the vaporized material onto the substrate. Sputtering not only suffers from the same disadvantages as evaporation but also requires additional consumables and equipment capable of generating the incident atoms.
The CVD process is similar to evaporation and sputtering but is distinguishable in that the deposited material undergoes a chemical reaction prior to deposition on a substrate. As with evaporation and sputtering, the CVD method requires high temperatures. Furthermore, although CVD can be performed at atmospheric as well as low pressures, the need for sophisticated equipment increases the cost of the process.
Thermal oxidation uses an oxygen atmosphere to oxidize an unpatterned layer of film previously deposited on a substrate in an unoxidized state. Unfortunately, like the processes above, thermal oxidation also requires the use of high temperatures.
Other methods, such as sol-gel and spin-on methods, include applying a precursor solution to a substrate to form a desired metal or metal-oxide film. Spin-coating or spin-casting may be used to apply the precursor solution and comprises dropping the precursor solution onto the middle of the substrate while it is rotated around its axis. The coated substrate is heated to a high temperature to convert the precursor film into a film of the desired material. The advantage of such methods over vapor-phase deposition is that the equipment requirements are less stringent. However, high temperatures are still required, as well as additional patterning steps, to obtain a pattern of the desired material.
In another method of forming patterned films, a photosensitive film is applied to a substrate and patterned. A conformal blanket of the desired material is then deposited on top of the patterned photosensitive material. A treatment that attacks the photosensitive material is applied to lift off both the photosensitive material and the attached overlying portion of the conformal blanket of desired material, thus leaving a patterned film of the desired material on the substrate. An advantage of this process is that an etching step is not required. Disadvantages include the fact that the process requires the additional steps of applying and patterning the photosensitive film. Further, pattern resolution is limited, which seriously hinders the usefulness of this method, since increasingly small features are becoming critical to modern applications.
In another method of forming patterned films, a conformal blanket of desired material is deposited over a channel that has been patterned into a substrate. The desired material fills and takes on the pattern of the channel, and the portion of the desired material outside the channel is removed, for example, by a process such as etching. A commonly used etching process is chemical mechanical planarization (“CMP”), which comprises applying a chemical agent with a slurry of abrasive particles to remove the desired material outside of the channel through a combination of chemical and mechanical action. Unfortunately, CMP requires expensive and complicated planarization equipment; extra consumable materials such as planarization pads, slurries and chemical agents; and extra processing steps to remove contaminants introduced by the process such as small slurry particles and etching chemicals.
Direct imaging methods have been used to pattern photoresist films. Photoresist is a lithographic material applied to the surface of a desired material as a step in existing patterning processes. The photoresist may be applied conventionally by spin coating, other solution-based coating methods, or by application of a dry film. Light is applied to the photoresist through a mask to form a predetermined pattern. The pattern formation occurs when the light changes the solubility of the exposed areas of the photoresist, and this change in solubility allows for the design of a selective development process. The undeveloped portion of the photoresist is then used as a pattern transfer medium or mask for etching the desired pattern into the desired material. The photoresist mask and any etch residues are then removed, and a patterned film of material remains on the substrate.
Negative direct imaging has also been applied to the deposition of metal-containing materials. This process comprises dissolving a metal organic complex in a suitable organic solvent to form a precursor solution. The precursor solution is then deposited on a substrate to form a film, and select portions are exposed to energy through, for example, use of a mask. The unexposed portions are then removed with a developer. Examples of such processes can be found in U.S. Pat. Nos. 5,534,312; and 6,071,676; and U.S. Patent Application Pub. No. U.S. 2002/0160103 A1, each of which are hereby incorporated herein in their entirety by reference.
One disadvantage of depositing metal-containing materials with negative direct imaging is that the materials used to form patterned films of metal-containing materials are limited to those that are soluble in a developer and that convert upon exposure to energy to a material that is insoluble in the developer. The problem is that some materials that adequately convert to an insoluble material upon exposure to energy are not very soluble in the developer in their unexposed form. As a result, harsh solvents are necessary to remove them, and these harsh solvents do not selectively develop only the unexposed portion of the film, but rather, they attack the converted material as well, thereby degrading the quality of the desired pattern to be formed.
Another disadvantage of negative direct imaging methods is that the amount of conversion is non-uniform. The energy scattering and attenuation that occurs during exposure of the metal-containing material may create a gradient in the degree of exposure across the thickness of the material, which accordingly results in a gradient in the degree of conversion of the material. As such, negative direct imaging creates a gradual change in the structure of the material across its thickness. This gradual change in structure creates differences in performance characteristics among the patterned metal-containing materials successively produced by the negative direct imaging method.
Accordingly, there is a need for a method of depositing metal-containing materials that is more cost effective, produces a more uniform product, and is capable of depositing a wider range of precursor materials.